1. Field of the Invention
The invention relates to an amplifier circuit and a magnetic sensor having reduced offset voltages.
2. Background Art
Instrumentation amplifiers are used to amplify weak output voltages of magnetic sensors, acceleration sensors, and the like.
High-precision and high gain are necessary for instrumentation amplifiers to amplify weak voltages; and direct current amplification by operational amplifiers is performed.
However, when offset voltages due to mismatch or temperature-related drift occur in the operational amplifier itself, the signal components of the amplified input signal cannot be discriminated, and high-precision amplification is impossible. Therefore, characteristics such as low drift and low offset are necessary for high-precision amplification; and there have been proposals including offset voltage adjustment circuits (for example, refer to JP-A 2006-174122 (Kokai)).
Also, signal detection circuits have been proposed to amplify the weak voltage of a Hall element and the like, set any detection threshold voltage, reduce the effects of the offset signal components included in the output, and perform a high-precision binary detection (for example, refer to JP-A 2008-236737 (Kokai)).